The present invention relates to a power semiconductor device having a main current section and an emulation current section that emulates, or follows, the current in the main current section.
Power semiconductor devices are devices designed to carry power level electrical current, such as current for powering an alternating current motor. It is often useful to limit the current in power devices for one of two basic reasons. First the power device may have an internal current limit above which the device switches into an undesirable mode of operation, possibly destructive to the power device. Second, the electrical system in which the power device is utilized may be able to tolerate only a particular maximum current level in the power device, above which deleterious circuit behavior results in the system.
In order to be able to limit current in a power semiconductor device, the device current level must first be sensed. One prior art technique of sensing current level in a power device involves sensing the voltage drop developed across a resistor that is serially connected to the power device. Unfortunately, the sensing resistor must be rated for a considerable level of power, and thereby results in an increased expense of current sensing.
Accordingly, an object of the present invention is to provide a power semiconductor device in which the device current level can be sensed with low power circuitry.
A further object of the invention is to provide a power semiconductor device in which the device current can be sensed economically and with high accuracy.
Another object of the invention is to provide a power semiconductor device in which low current emulation of the device current level is achieved without increasing the number of device fabrication steps.
In accordance with a preferred embodiment of the invention, there is provided a power semiconductor device having a plurality of active (i.e. current -carrying) region cells and a device termination region. A majority of the active region cells constitute a main current section and a minority of the active region cells constitute an emulation current section. The device termination region is common to, and surrounds both the main current section and the emulation current section in the preferred embodiment. A first cathode contacts the main current section, while a separate, second cathode contacts the emulation current section. A common anode contacts both the main current section and the emulation current section, and a gate is coupled to the main current section and, preferably, to the emulation current section.
The current level in the emulation current section closely emulates the current level in the main current section, owing to close thermal and electrical coupling between these sections, and, further, because they are formed in the same fabrication process. Since the current level in the emulation section constitutes only a fraction of that in the main current section, low power circuitry can be used to sense current in the power device by sensing current in the emulation section. Additionally, the present power device is only slightly more complex than a device without an emulation current section; accordingly, resulting economical current sensing is made possible by the present invention.